Add support for TCP_USER_TIMEOUT option.

The implementation follows the linux behavior where specifying
a TCP_USER_TIMEOUT will cause the resend timer to honor the
user specified timeout rather than the default rto based timeout.

Further it alters when connections are timedout due to keepalive
failures. It does not alter the behavior of when keepalives are
sent. This is as per the linux behavior.

PiperOrigin-RevId: 285099795

11 files changed, 343 insertions, 37 deletions

diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index d5bb5b6ed..f62fd729f 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -576,6 +576,11 @@ type KeepaliveIntervalOption time.Duration
 // closed.
 type KeepaliveCountOption int
 
+// TCPUserTimeoutOption is used by SetSockOpt/GetSockOpt to specify a user
+// specified timeout for a given TCP connection.
+// See: RFC5482 for details.
+type TCPUserTimeoutOption time.Duration
+
 // CongestionControlOption is used by SetSockOpt/GetSockOpt to set/get
 // the current congestion control algorithm.
 type CongestionControlOption string
diff --git a/pkg/tcpip/transport/tcp/BUILD b/pkg/tcpip/transport/tcp/BUILD
index 455a1c098..3b353d56c 100644
--- a/pkg/tcpip/transport/tcp/BUILD
+++ b/pkg/tcpip/transport/tcp/BUILD
@@ -28,6 +28,7 @@ go_library(
         "forwarder.go",
         "protocol.go",
         "rcv.go",
+        "rcv_state.go",
         "reno.go",
         "sack.go",
         "sack_scoreboard.go",
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index 74df3edfb..5422ae80c 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -242,6 +242,13 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 
 	n.initGSO()
 
+	// Now inherit any socket options that should be inherited from the
+	// listening endpoint.
+	// In case of Forwarder listenEP will be nil and hence this check.
+	if l.listenEP != nil {
+		l.listenEP.propagateInheritableOptions(n)
+	}
+
 	// Register new endpoint so that packets are routed to it.
 	if err := n.stack.RegisterTransportEndpoint(n.boundNICID, n.effectiveNetProtos, ProtocolNumber, n.ID, n, n.reusePort, n.boundBindToDevice); err != nil {
 		n.Close()
@@ -350,6 +357,14 @@ func (e *endpoint) deliverAccepted(n *endpoint) {
 	}
 }
 
+// propagateInheritableOptions propagates any options set on the listening
+// endpoint to the newly created endpoint.
+func (e *endpoint) propagateInheritableOptions(n *endpoint) {
+	e.mu.Lock()
+	n.userTimeout = e.userTimeout
+	e.mu.Unlock()
+}
+
 // handleSynSegment is called in its own goroutine once the listening endpoint
 // receives a SYN segment. It is responsible for completing the handshake and
 // queueing the new endpoint for acceptance.
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 3d059c302..4c34fc9d2 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -862,7 +862,7 @@ func (e *endpoint) resetConnectionLocked(err *tcpip.Error) {
 	}
 	e.state = StateError
 	e.HardError = err
-	if err != tcpip.ErrConnectionReset {
+	if err != tcpip.ErrConnectionReset && err != tcpip.ErrTimeout {
 		// The exact sequence number to be used for the RST is the same as the
 		// one used by Linux. We need to handle the case of window being shrunk
 		// which can cause sndNxt to be outside the acceptable window on the
@@ -1087,12 +1087,24 @@ func (e *endpoint) handleSegments() *tcpip.Error {
 // keepalive packets periodically when the connection is idle. If we don't hear
 // from the other side after a number of tries, we terminate the connection.
 func (e *endpoint) keepaliveTimerExpired() *tcpip.Error {
+	e.mu.RLock()
+	userTimeout := e.userTimeout
+	e.mu.RUnlock()
+
 	e.keepalive.Lock()
 	if !e.keepalive.enabled || !e.keepalive.timer.checkExpiration() {
 		e.keepalive.Unlock()
 		return nil
 	}
 
+	// If a userTimeout is set then abort the connection if it is
+	// exceeded.
+	if userTimeout != 0 && time.Since(e.rcv.lastRcvdAckTime) >= userTimeout && e.keepalive.unacked > 0 {
+		e.keepalive.Unlock()
+		e.stack.Stats().TCP.EstablishedTimedout.Increment()
+		return tcpip.ErrTimeout
+	}
+
 	if e.keepalive.unacked >= e.keepalive.count {
 		e.keepalive.Unlock()
 		e.stack.Stats().TCP.EstablishedTimedout.Increment()
@@ -1112,7 +1124,6 @@ func (e *endpoint) keepaliveTimerExpired() *tcpip.Error {
 // whether it is enabled for this endpoint.
 func (e *endpoint) resetKeepaliveTimer(receivedData bool) {
 	e.keepalive.Lock()
-	defer e.keepalive.Unlock()
 	if receivedData {
 		e.keepalive.unacked = 0
 	}
@@ -1120,6 +1131,7 @@ func (e *endpoint) resetKeepaliveTimer(receivedData bool) {
 	// data to send.
 	if !e.keepalive.enabled || e.snd == nil || e.snd.sndUna != e.snd.sndNxt {
 		e.keepalive.timer.disable()
+		e.keepalive.Unlock()
 		return
 	}
 	if e.keepalive.unacked > 0 {
@@ -1127,6 +1139,7 @@ func (e *endpoint) resetKeepaliveTimer(receivedData bool) {
 	} else {
 		e.keepalive.timer.enable(e.keepalive.idle)
 	}
+	e.keepalive.Unlock()
 }
 
 // disableKeepaliveTimer stops the keepalive timer.
@@ -1239,6 +1252,7 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 			w: &e.snd.resendWaker,
 			f: func() *tcpip.Error {
 				if !e.snd.retransmitTimerExpired() {
+					e.stack.Stats().TCP.EstablishedTimedout.Increment()
 					return tcpip.ErrTimeout
 				}
 				return nil
@@ -1405,6 +1419,7 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 		if s == nil {
 			break
 		}
+
 		e.tryDeliverSegmentFromClosedEndpoint(s)
 	}
 
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 4861ab513..dd8b47cbe 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -341,6 +341,7 @@ type endpoint struct {
 	// TCP should never broadcast but Linux nevertheless supports enabling/
 	// disabling SO_BROADCAST, albeit as a NOOP.
 	broadcast bool
+
 	// Values used to reserve a port or register a transport endpoint
 	// (which ever happens first).
 	boundBindToDevice tcpip.NICID
@@ -474,6 +475,12 @@ type endpoint struct {
 	// without hearing a response, the connection is closed.
 	keepalive keepalive
 
+	// userTimeout if non-zero specifies a user specified timeout for
+	// a connection w/ pending data to send. A connection that has pending
+	// unacked data will be forcibily aborted if the timeout is reached
+	// without any data being acked.
+	userTimeout time.Duration
+
 	// pendingAccepted is a synchronization primitive used to track number
 	// of connections that are queued up to be delivered to the accepted
 	// channel. We use this to ensure that all goroutines blocked on writing
@@ -1333,6 +1340,12 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		e.notifyProtocolGoroutine(notifyKeepaliveChanged)
 		return nil
 
+	case tcpip.TCPUserTimeoutOption:
+		e.mu.Lock()
+		e.userTimeout = time.Duration(v)
+		e.mu.Unlock()
+		return nil
+
 	case tcpip.BroadcastOption:
 		e.mu.Lock()
 		e.broadcast = v != 0
@@ -1591,6 +1604,12 @@ func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 		e.keepalive.Unlock()
 		return nil
 
+	case *tcpip.TCPUserTimeoutOption:
+		e.mu.Lock()
+		*o = tcpip.TCPUserTimeoutOption(e.userTimeout)
+		e.mu.Unlock()
+		return nil
+
 	case *tcpip.OutOfBandInlineOption:
 		// We don't currently support disabling this option.
 		*o = 1
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index 89b965c23..bc718064c 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -162,13 +162,26 @@ func (*protocol) HandleUnknownDestinationPacket(r *stack.Route, id stack.Transpo
 func replyWithReset(s *segment) {
 	// Get the seqnum from the packet if the ack flag is set.
 	seq := seqnum.Value(0)
+	ack := seqnum.Value(0)
+	flags := byte(header.TCPFlagRst)
+	// As per RFC 793 page 35 (Reset Generation)
+	//   1.  If the connection does not exist (CLOSED) then a reset is sent
+	//   in response to any incoming segment except another reset.  In
+	//   particular, SYNs addressed to a non-existent connection are rejected
+	//   by this means.
+
+	//   If the incoming segment has an ACK field, the reset takes its
+	//   sequence number from the ACK field of the segment, otherwise the
+	//   reset has sequence number zero and the ACK field is set to the sum
+	//   of the sequence number and segment length of the incoming segment.
+	//   The connection remains in the CLOSED state.
 	if s.flagIsSet(header.TCPFlagAck) {
 		seq = s.ackNumber
+	} else {
+		flags |= header.TCPFlagAck
+		ack = s.sequenceNumber.Add(s.logicalLen())
 	}
-
-	ack := s.sequenceNumber.Add(s.logicalLen())
-
-	sendTCP(&s.route, s.id, buffer.VectorisedView{}, s.route.DefaultTTL(), stack.DefaultTOS, header.TCPFlagRst|header.TCPFlagAck, seq, ack, 0 /* rcvWnd */, nil /* options */, nil /* gso */)
+	sendTCP(&s.route, s.id, buffer.VectorisedView{}, s.route.DefaultTTL(), stack.DefaultTOS, flags, seq, ack, 0 /* rcvWnd */, nil /* options */, nil /* gso */)
 }
 
 // SetOption implements TransportProtocol.SetOption.
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index 5ee499c36..0a5534959 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -50,16 +50,20 @@ type receiver struct {
 	pendingRcvdSegments segmentHeap
 	pendingBufUsed      seqnum.Size
 	pendingBufSize      seqnum.Size
+
+	// Time when the last ack was received.
+	lastRcvdAckTime time.Time `state:".(unixTime)"`
 }
 
 func newReceiver(ep *endpoint, irs seqnum.Value, rcvWnd seqnum.Size, rcvWndScale uint8, pendingBufSize seqnum.Size) *receiver {
 	return &receiver{
-		ep:             ep,
-		rcvNxt:         irs + 1,
-		rcvAcc:         irs.Add(rcvWnd + 1),
-		rcvWnd:         rcvWnd,
-		rcvWndScale:    rcvWndScale,
-		pendingBufSize: pendingBufSize,
+		ep:              ep,
+		rcvNxt:          irs + 1,
+		rcvAcc:          irs.Add(rcvWnd + 1),
+		rcvWnd:          rcvWnd,
+		rcvWndScale:     rcvWndScale,
+		pendingBufSize:  pendingBufSize,
+		lastRcvdAckTime: time.Now(),
 	}
 }
 
@@ -360,6 +364,9 @@ func (r *receiver) handleRcvdSegment(s *segment) (drop bool, err *tcpip.Error) {
 		return true, nil
 	}
 
+	// Store the time of the last ack.
+	r.lastRcvdAckTime = time.Now()
+
 	// Defer segment processing if it can't be consumed now.
 	if !r.consumeSegment(s, segSeq, segLen) {
 		if segLen > 0 || s.flagIsSet(header.TCPFlagFin) {
diff --git a/pkg/tcpip/transport/tcp/rcv_state.go b/pkg/tcpip/transport/tcp/rcv_state.go
new file mode 100644
index 000000000..2bf21a2e7
--- /dev/null
+++ b/pkg/tcpip/transport/tcp/rcv_state.go
@@ -0,0 +1,29 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcp
+
+import (
+	"time"
+)
+
+// saveLastRcvdAckTime is invoked by stateify.
+func (r *receiver) saveLastRcvdAckTime() unixTime {
+	return unixTime{r.lastRcvdAckTime.Unix(), r.lastRcvdAckTime.UnixNano()}
+}
+
+// loadLastRcvdAckTime is invoked by stateify.
+func (r *receiver) loadLastRcvdAckTime(unix unixTime) {
+	r.lastRcvdAckTime = time.Unix(unix.second, unix.nano)
+}
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 8332a0179..8a947dc66 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -28,8 +28,11 @@ import (
 )
 
 const (
-	// minRTO is the minimum allowed value for the retransmit timeout.
-	minRTO = 200 * time.Millisecond
+	// MinRTO is the minimum allowed value for the retransmit timeout.
+	MinRTO = 200 * time.Millisecond
+
+	// MaxRTO is the maximum allowed value for the retransmit timeout.
+	MaxRTO = 120 * time.Second
 
 	// InitialCwnd is the initial congestion window.
 	InitialCwnd = 10
@@ -134,6 +137,10 @@ type sender struct {
 	// rttMeasureTime is the time when the rttMeasureSeqNum was sent.
 	rttMeasureTime time.Time `state:".(unixTime)"`
 
+	// firstRetransmittedSegXmitTime is the original transmit time of
+	// the first segment that was retransmitted due to RTO expiration.
+	firstRetransmittedSegXmitTime time.Time `state:".(unixTime)"`
+
 	closed      bool
 	writeNext   *segment
 	writeList   segmentList
@@ -392,8 +399,8 @@ func (s *sender) updateRTO(rtt time.Duration) {
 
 	s.rto = s.rtt.srtt + 4*s.rtt.rttvar
 	s.rtt.Unlock()
-	if s.rto < minRTO {
-		s.rto = minRTO
+	if s.rto < MinRTO {
+		s.rto = MinRTO
 	}
 }
 
@@ -438,8 +445,30 @@ func (s *sender) retransmitTimerExpired() bool {
 	s.ep.stack.Stats().TCP.Timeouts.Increment()
 	s.ep.stats.SendErrors.Timeouts.Increment()
 
-	// Give up if we've waited more than a minute since the last resend.
-	if s.rto >= 60*time.Second {
+	// Give up if we've waited more than a minute since the last resend or
+	// if a user time out is set and we have exceeded the user specified
+	// timeout since the first retransmission.
+	s.ep.mu.RLock()
+	uto := s.ep.userTimeout
+	s.ep.mu.RUnlock()
+
+	if s.firstRetransmittedSegXmitTime.IsZero() {
+		// We store the original xmitTime of the segment that we are
+		// about to retransmit as the retransmission time. This is
+		// required as by the time the retransmitTimer has expired the
+		// segment has already been sent and unacked for the RTO at the
+		// time the segment was sent.
+		s.firstRetransmittedSegXmitTime = s.writeList.Front().xmitTime
+	}
+
+	elapsed := time.Since(s.firstRetransmittedSegXmitTime)
+	remaining := MaxRTO
+	if uto != 0 {
+		// Cap to the user specified timeout if one is specified.
+		remaining = uto - elapsed
+	}
+
+	if remaining <= 0 || s.rto >= MaxRTO {
 		return false
 	}
 
@@ -447,6 +476,11 @@ func (s *sender) retransmitTimerExpired() bool {
 	// below.
 	s.rto *= 2
 
+	// Cap RTO to remaining time.
+	if s.rto > remaining {
+		s.rto = remaining
+	}
+
 	// See: https://tools.ietf.org/html/rfc6582#section-3.2 Step 4.
 	//
 	// Retransmit timeouts:
@@ -1168,6 +1202,8 @@ func (s *sender) handleRcvdSegment(seg *segment) {
 		// RFC 6298 Rule 5.3
 		if s.sndUna == s.sndNxt {
 			s.outstanding = 0
+			// Reset firstRetransmittedSegXmitTime to the zero value.
+			s.firstRetransmittedSegXmitTime = time.Time{}
 			s.resendTimer.disable()
 		}
 	}
diff --git a/pkg/tcpip/transport/tcp/snd_state.go b/pkg/tcpip/transport/tcp/snd_state.go
index 12eff8afc..8b20c3455 100644
--- a/pkg/tcpip/transport/tcp/snd_state.go
+++ b/pkg/tcpip/transport/tcp/snd_state.go
@@ -48,3 +48,13 @@ func (s *sender) loadRttMeasureTime(unix unixTime) {
 func (s *sender) afterLoad() {
 	s.resendTimer.init(&s.resendWaker)
 }
+
+// saveFirstRetransmittedSegXmitTime is invoked by stateify.
+func (s *sender) saveFirstRetransmittedSegXmitTime() unixTime {
+	return unixTime{s.firstRetransmittedSegXmitTime.Unix(), s.firstRetransmittedSegXmitTime.UnixNano()}
+}
+
+// loadFirstRetransmittedSegXmitTime is invoked by stateify.
+func (s *sender) loadFirstRetransmittedSegXmitTime(unix unixTime) {
+	s.firstRetransmittedSegXmitTime = time.Unix(unix.second, unix.nano)
+}
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index bc5cfcf0e..2a83f7bcc 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -323,8 +323,8 @@ func TestTCPResetSentForACKWhenNotUsingSynCookies(t *testing.T) {
 		checker.SrcPort(context.StackPort),
 		checker.DstPort(context.TestPort),
 		checker.SeqNum(uint32(c.IRS+1)),
-		checker.AckNum(uint32(iss)+1),
-		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck)))
+		checker.AckNum(0),
+		checker.TCPFlags(header.TCPFlagRst)))
 }
 
 func TestTCPResetsReceivedIncrement(t *testing.T) {
@@ -460,18 +460,17 @@ func TestConnectResetAfterClose(t *testing.T) {
 			checker.TCP(
 				checker.DstPort(context.TestPort),
 				checker.SeqNum(uint32(c.IRS)+2),
-				checker.AckNum(790),
-				checker.TCPFlags(header.TCPFlagAck|header.TCPFlagRst),
+				checker.AckNum(0),
+				checker.TCPFlags(header.TCPFlagRst),
 			),
 		)
 		break
 	}
 }
 
-// TestClosingWithEnqueuedSegments tests handling of
-// still enqueued segments when the endpoint transitions
-// to StateClose. The in-flight segments would be re-enqueued
-// to a any listening endpoint.
+// TestClosingWithEnqueuedSegments tests handling of still enqueued segments
+// when the endpoint transitions to StateClose. The in-flight segments would be
+// re-enqueued to a any listening endpoint.
 func TestClosingWithEnqueuedSegments(t *testing.T) {
 	c := context.New(t, defaultMTU)
 	defer c.Cleanup()
@@ -576,8 +575,8 @@ func TestClosingWithEnqueuedSegments(t *testing.T) {
 		checker.TCP(
 			checker.DstPort(context.TestPort),
 			checker.SeqNum(uint32(c.IRS)+2),
-			checker.AckNum(793),
-			checker.TCPFlags(header.TCPFlagAck|header.TCPFlagRst),
+			checker.AckNum(0),
+			checker.TCPFlags(header.TCPFlagRst),
 		),
 	)
 }
@@ -914,7 +913,7 @@ func TestSendRstOnListenerRxAckV4(t *testing.T) {
 
 	checker.IPv4(t, c.GetPacket(), checker.TCP(
 		checker.DstPort(context.TestPort),
-		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck),
+		checker.TCPFlags(header.TCPFlagRst),
 		checker.SeqNum(200)))
 }
 
@@ -942,7 +941,7 @@ func TestSendRstOnListenerRxAckV6(t *testing.T) {
 
 	checker.IPv6(t, c.GetV6Packet(), checker.TCP(
 		checker.DstPort(context.TestPort),
-		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck),
+		checker.TCPFlags(header.TCPFlagRst),
 		checker.SeqNum(200)))
 }
 
@@ -4291,8 +4290,9 @@ func TestKeepalive(t *testing.T) {
 
 	c.CreateConnected(789, 30000, -1 /* epRcvBuf */)
 
+	const keepAliveInterval = 10 * time.Millisecond
 	c.EP.SetSockOpt(tcpip.KeepaliveIdleOption(10 * time.Millisecond))
-	c.EP.SetSockOpt(tcpip.KeepaliveIntervalOption(10 * time.Millisecond))
+	c.EP.SetSockOpt(tcpip.KeepaliveIntervalOption(keepAliveInterval))
 	c.EP.SetSockOpt(tcpip.KeepaliveCountOption(5))
 	c.EP.SetSockOpt(tcpip.KeepaliveEnabledOption(1))
 
@@ -4382,13 +4382,29 @@ func TestKeepalive(t *testing.T) {
 		)
 	}
 
+	// Sleep for a litte over the KeepAlive interval to make sure
+	// the timer has time to fire after the last ACK and close the
+	// close the socket.
+	time.Sleep(keepAliveInterval + 5*time.Millisecond)
+
 	// The connection should be terminated after 5 unacked keepalives.
+	// Send an ACK to trigger a RST from the stack as the endpoint should
+	// be dead.
+	c.SendPacket(nil, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: c.Port,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  790,
+		AckNum:  seqnum.Value(next),
+		RcvWnd:  30000,
+	})
+
 	checker.IPv4(t, c.GetPacket(),
 		checker.TCP(
 			checker.DstPort(context.TestPort),
 			checker.SeqNum(uint32(next)),
-			checker.AckNum(uint32(790)),
-			checker.TCPFlags(header.TCPFlagAck|header.TCPFlagRst),
+			checker.AckNum(uint32(0)),
+			checker.TCPFlags(header.TCPFlagRst),
 		),
 	)
 
@@ -6157,8 +6173,8 @@ func TestTCPTimeWaitDuplicateFINExtendsTimeWait(t *testing.T) {
 		checker.SrcPort(context.StackPort),
 		checker.DstPort(context.TestPort),
 		checker.SeqNum(uint32(ackHeaders.AckNum)),
-		checker.AckNum(uint32(ackHeaders.SeqNum)),
-		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck)))
+		checker.AckNum(0),
+		checker.TCPFlags(header.TCPFlagRst)))
 
 	if got := c.Stack().Stats().TCP.EstablishedClosed.Value(); got != want {
 		t.Errorf("got c.Stack().Stats().TCP.EstablishedClosed = %v, want = %v", got, want)
@@ -6336,7 +6352,147 @@ func TestTCPCloseWithData(t *testing.T) {
 		checker.SrcPort(context.StackPort),
 		checker.DstPort(context.TestPort),
 		checker.SeqNum(uint32(ackHeaders.AckNum)),
-		checker.AckNum(uint32(ackHeaders.SeqNum)),
-		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck)))
+		checker.AckNum(0),
+		checker.TCPFlags(header.TCPFlagRst)))
+}
+
+func TestTCPUserTimeout(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	c.CreateConnected(789, 30000, -1 /* epRcvBuf */)
+
+	origEstablishedTimedout := c.Stack().Stats().TCP.EstablishedTimedout.Value()
 
+	userTimeout := 50 * time.Millisecond
+	c.EP.SetSockOpt(tcpip.TCPUserTimeoutOption(userTimeout))
+
+	// Send some data and wait before ACKing it.
+	view := buffer.NewView(3)
+	if _, _, err := c.EP.Write(tcpip.SlicePayload(view), tcpip.WriteOptions{}); err != nil {
+		t.Fatalf("Write failed: %v", err)
+	}
+
+	next := uint32(c.IRS) + 1
+	checker.IPv4(t, c.GetPacket(),
+		checker.PayloadLen(len(view)+header.TCPMinimumSize),
+		checker.TCP(
+			checker.DstPort(context.TestPort),
+			checker.SeqNum(next),
+			checker.AckNum(790),
+			checker.TCPFlagsMatch(header.TCPFlagAck, ^uint8(header.TCPFlagPsh)),
+		),
+	)
+
+	// Wait for a little over the minimum retransmit timeout of 200ms for
+	// the retransmitTimer to fire and close the connection.
+	time.Sleep(tcp.MinRTO + 10*time.Millisecond)
+
+	// No packet should be received as the connection should be silently
+	// closed due to timeout.
+	c.CheckNoPacket("unexpected packet received after userTimeout has expired")
+
+	next += uint32(len(view))
+
+	// The connection should be terminated after userTimeout has expired.
+	// Send an ACK to trigger a RST from the stack as the endpoint should
+	// be dead.
+	c.SendPacket(nil, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: c.Port,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  790,
+		AckNum:  seqnum.Value(next),
+		RcvWnd:  30000,
+	})
+
+	checker.IPv4(t, c.GetPacket(),
+		checker.TCP(
+			checker.DstPort(context.TestPort),
+			checker.SeqNum(uint32(next)),
+			checker.AckNum(uint32(0)),
+			checker.TCPFlags(header.TCPFlagRst),
+		),
+	)
+
+	if _, _, err := c.EP.Read(nil); err != tcpip.ErrTimeout {
+		t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrTimeout)
+	}
+
+	if got, want := c.Stack().Stats().TCP.EstablishedTimedout.Value(), origEstablishedTimedout+1; got != want {
+		t.Errorf("got c.Stack().Stats().TCP.EstablishedTimedout = %v, want = %v", got, want)
+	}
+}
+
+func TestKeepaliveWithUserTimeout(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	c.CreateConnected(789, 30000, -1 /* epRcvBuf */)
+
+	origEstablishedTimedout := c.Stack().Stats().TCP.EstablishedTimedout.Value()
+
+	const keepAliveInterval = 10 * time.Millisecond
+	c.EP.SetSockOpt(tcpip.KeepaliveIdleOption(10 * time.Millisecond))
+	c.EP.SetSockOpt(tcpip.KeepaliveIntervalOption(keepAliveInterval))
+	c.EP.SetSockOpt(tcpip.KeepaliveCountOption(10))
+	c.EP.SetSockOpt(tcpip.KeepaliveEnabledOption(1))
+
+	// Set userTimeout to be the duration for 3 keepalive probes.
+	userTimeout := 30 * time.Millisecond
+	c.EP.SetSockOpt(tcpip.TCPUserTimeoutOption(userTimeout))
+
+	// Check that the connection is still alive.
+	if _, _, err := c.EP.Read(nil); err != tcpip.ErrWouldBlock {
+		t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrWouldBlock)
+	}
+
+	// Now receive 2 keepalives, but don't ACK them. The connection should
+	// be reset when the 3rd one should be sent due to userTimeout being
+	// 30ms and each keepalive probe should be sent 10ms apart as set above after
+	// the connection has been idle for 10ms.
+	for i := 0; i < 2; i++ {
+		b := c.GetPacket()
+		checker.IPv4(t, b,
+			checker.TCP(
+				checker.DstPort(context.TestPort),
+				checker.SeqNum(uint32(c.IRS)),
+				checker.AckNum(uint32(790)),
+				checker.TCPFlags(header.TCPFlagAck),
+			),
+		)
+	}
+
+	// Sleep for a litte over the KeepAlive interval to make sure
+	// the timer has time to fire after the last ACK and close the
+	// close the socket.
+	time.Sleep(keepAliveInterval + 5*time.Millisecond)
+
+	// The connection should be terminated after 30ms.
+	// Send an ACK to trigger a RST from the stack as the endpoint should
+	// be dead.
+	c.SendPacket(nil, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: c.Port,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  790,
+		AckNum:  seqnum.Value(c.IRS + 1),
+		RcvWnd:  30000,
+	})
+
+	checker.IPv4(t, c.GetPacket(),
+		checker.TCP(
+			checker.DstPort(context.TestPort),
+			checker.SeqNum(uint32(c.IRS+1)),
+			checker.AckNum(uint32(0)),
+			checker.TCPFlags(header.TCPFlagRst),
+		),
+	)
+
+	if _, _, err := c.EP.Read(nil); err != tcpip.ErrTimeout {
+		t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrTimeout)
+	}
+	if got, want := c.Stack().Stats().TCP.EstablishedTimedout.Value(), origEstablishedTimedout+1; got != want {
+		t.Errorf("got c.Stack().Stats().TCP.EstablishedTimedout = %v, want = %v", got, want)
+	}
 }